<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #acc{
            color: gray;
        }
    </style>
</head>
<body>
    <input type="text"  id="acc" value="请输入您的账户信息" onkeydown="keyDown()" onkeyup="keyUp()">
    <input type="text" placeholder="请输入">
    <script>
        function keyDown(){
            var acc = document.getElementById("acc")
            if(acc.value == "请输入您的账户信息"){
                acc.value = "";
                acc.style.color = "black"
            }
        }
        function keyUp(){
            var acc = document.getElementById("acc")
            if(acc.value == ""){
                acc.value = "请输入您的账户信息"
                acc.style.color = "gray"
            }
        }
    </script>
</body>
</html>